This invention relates to a power amplifier, particularly a power amplifier for use in various audio circuits.
In an audio output stage of an audio apparatus, such as used in a television receiver, a power amplifying circuit amplifies an audio signal so that the audio signal can drive a loudspeaker. Usually, from the viewpoint of power efficiency, the power amplifying circuit employs a class B power amplifying circuit which comprises a push-pull transistor output circuit and a driving circuit driving the output circuit. This type of power amplifying circuit normally is pre-driven by a pre-driving circuit in response to an audio input signal; the pre-driving circuit usually comprises a class A amplifying circuit. Furthermore, the pre-driving circuit supplies a pre-driving current to the driving circuit of the power amplifying circuit. In the prior art, the pre-driving circuit generates a constant pre-driving current corresponding to the maximum pre-driving current for the driving circuit irrespective of the level of the incoming audio signal. Accordingly, the pre-driving circuit wastefully consumes power.